Most likely forged because the Arts College he was rejected by had consisted primarily of Jewish Professors, one of them reviewed (and rejected) his application.
This leads to him being a soldier (due to no money), then getting imprisoned, then writing Mein Kampf where he even says himself he hates Jews (as well as providing his back story) and so on.

"Corporal Hitler was a dispatch runner, taking messages back and forth from the command staff in the rear to the fighting units near the battlefield."

I'd say he got in contact with the enemy from time to time since he was on the front between 1914 when the war started to october 1916 and then again in march 1917 to october 1918. That's a total of about three years on the frontline of a full on war, I don't think anyone can go that long without killing a few enemies since he was just as armed as other soldiers.

Actually, the man who has killed more people on his lifetime is a soviet officer who Stalin appointed. He went to "work" with a briefcase full of guns and had people reloading them all the time while he executed people who weren't loyal to the revolution.
Around 50,000 people.